This invention relates generally to an apparatus for steering the rear wheels of a vehicle.
It is known to modify automotive vehicle steering characteristics by including rear-wheel steering systems. Such rear wheel steering systems are designed to augment the vehicle steering function that conventional front-wheel steering systems provide. Some rear-wheel steering systems include multi-link solid axle suspensions having track bars or xe2x80x9cpan-hard rodsxe2x80x9d that pivotally connect a vehicle frame to the axle to minimize ride steer caused by relative vertical motion between a vehicle frame and the axle.
For example, U.S. Pat. No. 5,820,147 issued Oct. 13 1998 to Rohweder et al., discloses a rear wheel steering apparatus including a vehicle frame and a multi-link suspension including a live solid axle and a track bar or pan hard rod connected between the axle and the vehicle frame and a pair of road wheels supported at respective opposite ends of the axle by first and second steering knuckles, the knuckles supporting the road wheels for rotation about respective generally horizontal road wheel rotational axes and for pivotal motion about respective generally vertical steering axes. The rear wheel steering apparatus of the Rohweder et al. patent includes first and second steering arms extending from the respective first and second steering knuckles in a direction generally perpendicular to the respective steering axes and a drag link having a first end connected to a tie rod that extends between and interconnects respective outer ends of the steering arms. The rear wheel steering apparatus disclosed in the Rohweder et al. patent also includes a steering gear having a pitman arm connected to a second end of the drag link and configured to pivot the roadwheels about their respective pivot axes by alternately pushing and pulling on the drag link. However, a rear wheel steering apparatus constructed according to the Rohweder et al. patent requires a primary connection to a handwheel and thus is not readily adaptable to steering rear road wheels that are remote from the vehicle handwheel.
It is also known for rear wheel steering systems to employ linear steering actuators. U.S. Pat. No. 5,899,292 issued May 4, 1999 to Paul et al., discloses a hydraulic drive and steering system for a vehicle that includes rear road wheel steering arms extending from respective steering knuckles and two linear actuators connected between a frame of the vehicle and respective outer ends of the steering arms to allow an operator to steer the rear road wheels using a handwheel without a primary connection between the handwheel and the rear road wheels. However, a rear wheel steering apparatus constructed according to the Paul et al. patent cannot be incorporated into existing multi-link suspension systems without changing existing suspension geometry.
As shown in FIG. 1 in the drawings, the prior art also includes a front wheel drive system 10 having a solid axle 11 and including a linear power steering actuator 12 that connects to a drag link 14. The drag link 14 connects to a pair of steering arms 16 extending from a pair of steering knuckles 18. Extension and retraction of the power steering actuator 12 alternately pushes and pulls on the drag link 14 resulting in steering inputs to a pair of front road wheels 20 connected to the steering knuckles. The system relies on a primary connection to a hand wheel input and would be difficult to adapt for use in steering rear wheels mounted remote from the hand wheel input on a live rear axle of a vehicle in a multi-link suspension.
What is needed is a steering apparatus that can steer road wheels mounted on a rear axle of a vehicle without requiring a primary connection to the handwheel. What is also needed is such a rear wheel steering apparatus that can be incorporated into existing multi-link suspension designs without changing existing suspension geometry.
A rear wheel steering apparatus for steering the rear wheels of a vehicle is provided that includes a multi-link suspension including a live axle and a track bar pivotally connecting the axle to a vehicle frame. First and second steering knuckles are supported at respective opposite ends of the axle and are configured to support respective road wheels for rotation about respective generally horizontal road wheel rotational axes and for pivotal motion about respective generally vertical steering axes. The rear wheel steering apparatus also includes first and second steering arms that extend generally horizontally from the respective first and second steering knuckles in a direction generally perpendicular to the respective steering axes. A drag link extends between and interconnects respective outer ends of the steering arms, the ends of the arms being spaced from the respective steering knuckles.
Unlike the prior art, the rear wheel steering apparatus also includes an actuator having a first end connected to the frame and a second end connected to the drag link. The actuator is positioned and configured to pivot the roadwheels about their respective steering axes by alternately pushing and pulling on the drag link. Therefore, a rear wheel steering apparatus constructed according to the invention is able to steer road wheels mounted on a rear axle of the vehicle that is remote from the vehicle handwheel without requiring a primary connection to the handwheel. The apparatus may be readily incorporated into existing multi-link suspension designs without changing existing suspension geometry.